Vitreous materials are generally manufactured from a mixture of raw materials, for example silicates, basalt, limestone, soda ash and other minor constituents which are introduced into a melter and melted into a viscous liquid state at temperatures in the order of 1250 to 1500° C.; the melt is then supplied to a forming process. Depending on the intended use of the melt, for example for manufacture of flat glass, hollow glass, continuous fibers for reinforcement purposes or fibers for insulation purposes, an appropriate further melt refining step may be required upstream of the forming process. The chemical composition of the melt and its physical properties are selected as a function of the intended use and the forming process.
Conventional glass melters comprise an energy supply from above a glass melt surface, for instance from burners generating a flame in a space between the glass melt surface and a crown of the melter, whereby heat is transferred to the glass melt by the flame itself and by radiation from the crown material. Raw batch material to be melted is loaded at the top of the glass melt in the melter and heat is transferred from the melt to the batch material which is incorporated into the melt.
In some glass melters, energy is supplied by electrically heated electrodes arranged below the surface of the melt; such electrodes may provide the only heat source or be used in combination with burners.
Glass melters used to manufacture stone wool insulation have traditionally been cupola furnaces.
In submerged combustion melting raw materials are generally melted by introducing fuel gas and oxygen containing gas through the mass of molten material, causing said fuel gas and oxygen to mix and burn within said mass, melting additional raw material by the heat generated by the burning gas mixture. In an alternative, fuel gas and air and/or oxygen are burned outside the said mass and the hot combustion gases are blown into the glass melt.
Conventional burners used for submerged combustion generally produce a flame that shows a tendency to become unstable, particularly under extreme conditions of agitation in a glass melt. Conventional burners either burn the fuel gas and the oxidant in a combustion chamber and blow the combustion gases into the glass melt, or blow the fuel gas and the oxidant through concentric tubes into the glass melt for combustion therein.
Conventional burners for submerged combustion melting of vitrifiable material generally comprise concentric pipe burners, also called tube-in-tube burners. The inner tube generally is designed for blowing the fuel gas and the outer tube is designed for blowing the oxidant.